Method and apparatus for checking the superimposition of an x-ray field and a lightfield

ABSTRACT

A method and apparatus is disclosed for checking the alignment of various interfaced components in a conventional x-ray system. The disclosed method functions to verify the coincidence of the x-ray field, emanating from the x-ray apparatus, with the target lightfield, projecting from the x-ray collimator. If these two fields are coincident within an allowable tolerance, the x-ray apparatus, collimator and film cassette carrier are properly aligned for that particular source-to-image distance. The apparatus includes a plurality of target plates having a width equal to the allowable tolerance for the particular source-toimage distance. The method includes the steps of projecting the lightfield over the target area, and centrally positioning the plurality of target plates on the peripheral edges of the lightfield. An x-ray beam is then projected onto the film located in the target area. The exposed x-ray film is then examined to determine whether a portion of each of the target plates is located on the x-ray field. If one or more of the target plates is not located on the exposed x-ray film, the x-ray field is not superimposed on the lightfield within the allowable tolerance. The x-ray apparatus is then realigned with the collimator and the test procedure is repeated until a portion of all four target plates is located on the exposed x-ray film to denote proper alignment.

United States Patent 11 1 Redfield et al.

[ METHOD AND APPARATUS FOR CHECKING THE SUPERIMPOSITION OF AN X-RAYFIELD AND A LlGHTFlELD [75] Inventors: Charles L. Redfield, Woodridgc;

Robert G. Schultz; Arne Van Art, both of Elmhurst, all of Ill.

[73] Assignee: Litton Medical Products, lne., Elk

Grove Village. Ill.

22 Filed: Sept. 16, [974 21 App]. No.: 506,258

[52] US. Cl. 250/49l; 250/511; 250/476 [51] Int. (1 GOlN 21/00; GI 18l/()(); GZIF 5/04 [58] Field of Search 250/476, 5] l, 5l2, 5l3, 250/491,252

[56} References Cited UNITED STATES PATENTS 115K824 1 H1964 Peyser250/51] Primary Erumiuer-Jamcs W. Lawrence Ari-ism! E.\'umiuer'T. N.Grigsb Attorney, Ageul, or FirmRobcrt M. Vargo; Alan C. Rose {57}ABSTRACT A method and apparatus is disclosed for checking the Sept. 30,1975 alignment of various interfaced components in a conventional x-raysystem. The disclosed method func tions to verify the coincidence of thex-ray field, emanating from the x-ray apparatus, with the target lightfield, projecting from the x ray collimator. If these two fields arecoincident within an allowable tolerance, the x-ray apparatus,collimator and film cassette carrier are properly aligned for thatparticular sourcetoimage distance The apparatus includes a plurality oftarget plates having a width equal to the allowable tolerance for theparticular source-to-image distance. The method includes the steps ofprojecting the lightfield over the target area, and centrallypositioning the plurality of target plates on the peripheral edges ofthe lightfield. An x-ray beam is then projected onto the film located inthe target area. The exposed x-ray film is then examined to determinewhether a portion of each of the target plates is located on the x rayfield. If one or more of the target plates is not located on the exposedx-ray film, the x-ray field is not superimposed on the lightfield withinthe allowable tolerance, The x-ray apparatus is then realigned with thecollimator and the test procedure is repeated until a portion of allfour target plates is located on the exposed x-ray film to denote properalignment.

9 Claims, 3 Drawing Figures US. Patent Sept. 30,1975 3,909,616

METHOD AND APPARATUS FOR CHECKING THE SUPERIMPOSITION OF AN X-RAY FIELDAND A LIGI-ITFIELD BACKGROUND OF THE INVENTION 1. Field of the InventionThe present invention relates to a method and apparatus for checking thealignment of various components in a conventional medical x-ray systemand more particularly to a method and apparatus for verifying thecoincidence of the x-ray field with the target lightfield.

2. Description of the Prior Art Under the new Bureau of RadiologicalHealth (hereinafter called BRH) standards, which have been in effectsince Aug. 1, 1974, the xray field, established by the x-rays emanatingfrom an x-ray apparatus onto a target area, must be coincident with thetarget lightfield, projecting from the x ray collimator, within acertain tolerance. It has been established that this tolerance (thedistance the peripheral edge of the xray field can deviate from themating peripheral edge of the target lightfield) must be two percent orless of the x-ray source-to-image distance (hereinafter called SID). Forexample, for an SID of 40 inches, the tolerance would be 0.8 inches.

Although one of the reasons for having the lightfield and x-ray fieldcoincident is to properly align the x-ray apparatus with the collimator,the main reason for the coincidence is to ensure that the patients arenot unduly exposed to a broader dosage of x-rays than is necessary tocover the x-ray film used in the exposure. Therefore, the cruxof the newBRH standards is patient safety.

Heretoforc. a complex procedure has been utilized for aligning the x-rayapparatus with the x-ray collima tor. This aligning procedure consistedof mounting a piece of ready pack film over the target area andprojecting the collimator lightfield onto the ready pack film envelope.A plurality of pinholes are then inserted through the film envelope atthe periphery of the light beam to designate the lightfield when film isdeveloped. An x-ray exposure is then taken. Upon examining the exposure.the edges of the x-ray field are determined (the area denoting 25percent maximum density) and the distance between the pinholes, denotingthe lightfield edges, and the edges of the x-ray field are thenphysically measured. It is then necessary to calculate whether thisdistance is greater or less than 2 percent of the given SID (theallowable tolerance). The shortcoming with this system is that physicalmeasurements must be taken and mental calculations must be made, which,of course, are susceptible to errors.

SUMMARY OF THE INVENTION The present invention obviates theabove-mentioned shortcomings by providing an x-ray components alignmentmethod and apparatus that eliminates the need for physical measurementsand mental calculations.

In its broadest aspect, the method includes the steps of locking thex-ray apparatus and collimator in position over the target area at aspecific SID. The square or rectangular lightfield from the collimatoris then projected on the target area. A special target piece is thencentrally positioned on each of the peripheral edges forming the outlineof the lightfield. Each target piece forming the test apparatus is aplate having a pair of indices equal to the allowable tolerance of thex-ray field with respect to the lightfield at the specific SID. Afterthe target pieces are centrally placed on the edges of the lightfield,an exposure is made on the x-ray film. Upon developing the film, thefilm is examined to determine if portions of all four target piecesappear on the film. If this is accomplished, then the x-ray andlightfields are coincident, and no alignment readjustment between thex-ray apparatus and collimator is necessary. If one or two of the targetpieces do not appear on the exposed film, this would signify that thedistances between the lightfield edges and the x-ray field edges weregreater than the allowable tolerance for that particular SID. When thisoccurs, adjustments between the x-ray apparatus and the collimator haveto be made and the entire test procedure repeated.

The primary advantage of the present invention is that the entire testmethod can be accomplished expeditiously and accurately.

The features of the present invention, which are believed to be novel,are set forth with particularity in the appended Claims. The presentinvention, both as to its organization and manner of operation, togetherwith the further advantages thereof may best be understood by referenceto the following description taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of anx-ray system utilizing the apparatus of the present invention;

FIG. 2 is an isometric view of one of the target plates utilized in thepresent invention,

FIG. 3 is a plan view of the target area of the x-ray system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings, FIG. I illustrates a typical medical x-ray system, generallyindicated by arrow 10 consisting of an x-ray apparatus 11, a collimatorI3 and a target area 15. These components can be of any conventionaldesign, and the apparatus of the present invention can be utilized onany x-ray equipment ensemble.

As with all conventional x-ray systems, the x-ray apparatus 11 functionsto emit a quantity of x-rays onto the target area with the collimator I3functioning to constrain the x-ray beam to a given size. The collimator13 also includes a light emmitter (not shown) for projecting a field oflight 17 onto the target area 15. The purpose of the lightfield is toindicate to the operator where the x-ray field will be located duringthe desired exposure. The target area usually includes a bucky movablysupporting a film cassette for one or more exposures. The patient to bex-rayed would be located between the target area and the x-rayapparatus.

As stated previously, the purpose of the present invention is to insurethat for each SID, the x-ray field is coincident with the lightfield I7within the BRH tolerance.

In accordance with the present invention, a plurality of target plates20, 2|, 22 and 23 are provided to be positioned on the peripheral edgesof the lightfield 17. As shown more clearly in FIG. 2, each target plateis rectangular in shape and includes a pair of centering notches 24which function as a guide for centering the target plate onto arespective peripheral edge of the lightfield 17.

The width of the target plate is denoted by the letter d and is equal tothe amount of tolerance of the x-ray field with respect to thelightfield for a particular SlD. As in the previous example, if the SlDwere 40 inches, the amount of allowable tolerance or width of the targetplate would be 0.8 inches.

As shown in FIG. 3, the set of four target plates 20, 2 l 22 and 23 isutilized, with one target plate being positioned on each peripheral edgeof the lightfield 17. it would be noted that the lightfield andsuperimposed x-ray field can be either square or rectangular in shapedepending on the type of x-ray taken.

OPERATION In operation, the x-ray apparatus 11 is fixed with respect tothe collimator 13. During the test period, it is preferable to positiona sheet of paper over the target area 15 in order that the lightfieldcan be more easily seen. After the paper is inserted on the target area15, the collimator light is turned on to project the lightfield 17 ontothe paper of target area 15. The desired set of target plates 20, 21, 22and 23 for that particular SID are centrally positioned on theperipheral edges of the lightfield l7. Afterwards, the x-ray beam fromthe x-ray apparatus 11 is projected onto the target area [5. Forillustrative purposes, the outline of the exposed x-ray field is shownby the numeral 25. The next step of the procedure is to develop theexposed x-ray film and examine it to determine the outline of the x-rayfield. In practice, the x-ray field outline is determined by the linesequal to 25 percent of the maximum density of the x-ray. The x-ray isthen further examined to determine whether a portion of each of thetarget plates 20, 21, 22 and 23 is located on the peripheral edges ofthe x-ray field 25. in the example shown, only the target plates 20 and21 appear on the x-ray film, while the target plates 22 and 23 arecompletely absent therefrom. This would mean that the x-ray field is notsufficiently coincident with the lightfield 17 within the allowable BRHtolerance. The x-ray apparatus 11 would then have to be adjusted withrespect to the collimator l3, and the test procedure would have to berepeated until a film exposure is taken in which all four target plates20, 2] 22 and 23 appear on the peripheral edges of the x-ray field 25.Once this is accomplished, the x-ray field will be properly positionedwith respect to the lightfield 17 within the allowable BRH standards.This procedure would then be repeated for the other SlDs with differentsets of target plates being used for the different SlDs. As can be seen,no physical measurements or mental calculations are required for thistest procedure, and the entire operation can be handled more easily andquickly than prior systems.

It should be noted that various modifications can be made to theassembly while still remaining within the purview of the followingclaims. For example, a plurality of pairs of indices can be utilized oneach target plate, with each pair of indices representing the allowabletoleranee for a respective SID.

What is claimed is:

l. In an x'ray system which includes a target area having a filmcassette mounted thereon, an x-ray apparatus having a source of x-rays,located a specific distance from said target area, for emitting a beamof xrays onto said target area, and a collimator having a light emitterfor projecting a light beam onto said target area, a method for checkingthe superimposition of the x-ray field and the lightfield on said targetarea comprising the steps of: projecting a lightfield on said targetarea; positioning a plurality of target pieces on the outline of saidlightfield, said target pieces each having a pair of indices equal tothe allowable tolerance of the x-ray field position with respect to thelightfield position at the specific source-to-target area distance;

projecting an x-ray field onto said target area; and

developing and examining said exposed film located on said target areato determine whether a portion of each target piece is located on theoutline of the x-ray field.

2. The method of claim 1 wherein each target piece is centrallypositioned on the lines forming the outline of said lightfield.

3. The method of claim I wherein said lightfield is square orrectangular and one target piece is positioned on each of the four linesforming the outline of said lightfield.

4. The method of claim 1 further including the step of mounting a pieceof paper over said target area to enable the lightfield to be morevisible.

5. In an x-ray system which includes a target area having a filmcassette mounted thereon, an x-ray apparatus having a source of x-rays,located a specific distance from said target area, for emitting a beamof xrays onto said target area, and a collimator having a light emitterfor projecting a light beam onto said target area, an apparatus forchecking the superimposition of the x-ray field and the lightfield onsaid target area comprising:

a plurality of target pieces, said target pieces each having a pair ofindices equal to the allowable tolerance of the x-ray field positionwith respect to the lightfield position at the specific source-to-targetarea distance.

6. The combination of claim 5 wherein each target piece has a widthequal to said allowable tolerance.

7. The combination of claim 5 wherein each target piece is a rectangularplate.

8. The combination of claim 5 wherein each target piece includes a pairof centering notches bisecting the width of each piece.

9. The combination of claim 5 wherein the plurality of target piecesnumber four.

I k i l

1. In an x-ray system which includes a target area having a filmcassette mounted thereon, an x-ray apparatus having a source of x-rays,located a specific distance from said target area, for emitting a beamof x-rays onto said target area, and a collimator having a light emitterfor projecting a light beam onto said target area, a method for checkIngthe superimposition of the x-ray field and the lightfield on said targetarea comprising the steps of: projecting a lightfield on said targetarea; positioning a plurality of target pieces on the outline of saidlightfield, said target pieces each having a pair of indices equal tothe allowable tolerance of the x-ray field position with respect to thelightfield position at the specific source-to-target area distance;projecting an x-ray field onto said target area; and developing andexamining said exposed film located on said target area to determinewhether a portion of each target piece is located on the outline of thex-ray field.
 2. The method of claim 1 wherein each target piece iscentrally positioned on the lines forming the outline of saidlightfield.
 3. The method of claim 1 wherein said lightfield is squareor rectangular and one target piece is positioned on each of the fourlines forming the outline of said lightfield.
 4. The method of claim 1further including the step of mounting a piece of paper over said targetarea to enable the lightfield to be more visible.
 5. In an x-ray systemwhich includes a target area having a film cassette mounted thereon, anx-ray apparatus having a source of x-rays, located a specific distancefrom said target area, for emitting a beam of x-rays onto said targetarea, and a collimator having a light emitter for projecting a lightbeam onto said target area, an apparatus for checking thesuperimposition of the x-ray field and the lightfield on said targetarea comprising: a plurality of target pieces, said target pieces eachhaving a pair of indices equal to the allowable tolerance of the x-rayfield position with respect to the lightfield position at the specificsource-to-target area distance.
 6. The combination of claim 5 whereineach target piece has a width equal to said allowable tolerance.
 7. Thecombination of claim 5 wherein each target piece is a rectangular plate.8. The combination of claim 5 wherein each target piece includes a pairof centering notches bisecting the width of each piece.
 9. Thecombination of claim 5 wherein the plurality of target pieces numberfour.